Nonwoven fabrics and the method of manufacture thereof



United States Patent ABSTRACT OF THE DISCLOSURE A nonwoven fabric ismade by forming an open, nonwoven web of staple fibres or continuousfilaments, electrostatically projecting potentially crimpable flockfibres into the web and developing the crimp in the flock fibres toentangle them with the web fibres. Either the flock fibres or web fibresor both may be heterofilaments having a potentially adhesive componentwhich is bonded to the neighboring fibres at the cross-over points.

DISCLOSURE This invention relates to nonwoven fabrics and, inparticular, to nonwoven fabrics comprising an open web the fibres inwhich are bonded together by short length textile fibres, the fibresbeing projected into the web by the action of an electrostatic field.

Many processes for binding the fibres in a web together to yield anon-woven fabric having a degree of strength are known to the art. Thusfibres in webs may be bonded together by applying an adhesive to thewhole or selected parts of the web, by needle punching or, where the webcontain potentially adhesive fibres, by causing the potentially adhesivefibres to become tacky and bond themselves to other fibres in the web atpoints of contact.

We have now found that particularly attractive and novel fabrics can beobtained by electrostatically projecting short length staple fibres,generally known as flock, into an open web of fibres and then causingthe flock fibres to crimp and bond the web together.

According to one aspect of the present invention therefore there isprovided a nonwoven fabric comprising a web the fibres in which arebonded together by crimped flock, the fibres of the flock having anuncrimped length no greater than 4 inch.

The most desirable results from the standpoint of tensile strength inthe resulting fabric are obtained when the fibres of the flock have acrimp frequency not less than 20 crimps per inch.

In the specification the term bonded includes bonding by fibreentanglement, bonding by fusion and bonding by chemical adhesion broughtabout by rendering one component of the fabric tacky by the addition ofsome substance, e.g., a solvent, which can subsequently be removed tocause that compenent to revert to the nontacky state, but does notinclude bonding which is the result of the deliberate addition of anadhesive to the web.

The fabrics of this invention can be manufactured by projecting flock,com-prising potentially crimpable fibres, which may contain apotentially adhesive component into an open fibrous web, by the actionof electrostatic forces. The web may be composed of staple length fibresor of continuous filament components and may also contain a significantproportion of a potentially adhesive component. The fibres in the webare then bonded together by causing the flock to crimp and thus becomeentangled with the web fibres to give a nonwoven fabric of somestrength. The fabric may be further strengthened by causing the po-3,377,232 Patented Apr. 9, 1968 tentially adhesive component of theflock to become tacky and bond the fibres in the web and flock togetherat their crossover points.

The flock employed may be composed of heterofilament fibres in which onecomponent of the heterofilament is potentialy adhesive, in which caseparticularly good bonding of the flock onto the web is obtained.

The web may also be composed of heterofilaments, in staple fibre form ifrequired, in which one component is potentially adhesive.

Suitable heterofilaments for flock or web fibres may be in the formwhere the components exist in a side-by-side or sheath and corerelationship, in the latter instance of course the potentially adhesivecomponent will be the sheath components.

Accordingly, from another aspect the present invention provides aprocess for the manufacture of fabrics wherein flock composed ofpotentially crimpable fibres is projected into fibrous web by the actionof electrostatic forces and the structure obtained treated to cause theflock fibres to crimp and thereby bond together fibres inthe fibrousweb, by entanglement of the fibres of the flock with fibres of the web.

When the flock fibres contain a potentially adhesive component, it maybe rendered tacky, thereby further strengthening the fabric, in the sametreatment by which the flock fibres are crimped or in a subsequenttreatment.

In order to improve the penetration of the flock into the web, the flockmay be forced further into the web by mechanical means, for-example, byrolling, preferably whilst still subject to the action of theelectrostatic forces. Any of the flock fibres which have not penetratedsufficiently into the web may then be removed by a vacuum extractorbefore the fabric is further treated.

To give added strength to the fabric, flock may be projected into bothfaces of the web before treating the fabric to crimp the fibres in theflock.

The invention will now be more fully described, in the followingexamples, which examples are by way of illustration only and are in noway intended to be limitative.

EXAMPLE 1 A carded open web of 1% inch staple fibres ofpolyhexamethylene adipamide having a weight of 4 ounces per square yardis laid on the earthed working top of a conventional flocking unit andbelow a flock container, comprising a sieve and a brush, which ischarged by a high tension source at 110 kv. The unit is also providedwith a roller and vacuum extractor. Flock for this experiment consistsof 3 mm. staple fibres cut from heterofilaments composed of 66 nylon and66/6 (/20) nylon copolymer components existing in a side-by-siderelationship.

The flock, is fed to the sieve, distributed uniformly by the brushes,allowed to fall into the electric field maintained between the chargedcontainer and the earthed working top, and projected into the staplefibre web. The web is then rolled using an insulated roller whilst underthe influence of the electric field, to press the fibres further intothe web. Flock which has not penetrated into the web is removed by thevacuum extractor. Examination of the web at this stage shows that theflock fibres in the web are oriented within the web in a directionsubstantially perpendicular to the plane of the web.

The web is immersed in boiling water for 3 minutes to cause the flockfibres to crimp and entangle themselves into the web. The crimped flockpossesses a crimp frequency of approximately 25 per inch. At this stagethe fabric has some strength owing to the mechanical bonding effect ofthe crimped flock in the web, but on handling tends to shed flock. Tobond the flock firmly in the web,

EXAMPLE 2 The process of Example 1 was repeated to give fabricscontaining various percentages of flock. The percentage fiock in thefabric and'the tenacity of the fabric are given in Table 1.

TABLE 1 Denier of Fabric Tenacity of Fabric, g./d.

Percentage Flock in Fabric:

Fabrics containing more than about 45% of flock tend to have a harshhandle and relatively poor drape.

The heterofilament flock may be crimped by means other than immersion inboiling water, thus it may be subjected to a steam treatment, or dryheated, or to a chemical treatment. If superheated steam is used and thepotentially adhesive component of the heterofilament has a sufficientlylow melting, then the crimping and bonding steps can be carried outsimultaneously.

Variations in the handle and surface effect of flocked web and can beobtained by applying other processes, e.g. needle punching to theflocked web before the bonding operation. v

The invention is not limited to the use of webs or flock based only onpolyamides; any suitable materials may be employed provided thateffective bonding between the flock and the web can be attained, i.e.the potentially adhesive component where employed should be compatiblewith the other components of the fabric.

What we claim is:

1'. A nonwoven fabric in the form of an open, nonwoven, fibrous webhaving crimped flock fibres embedded within the body of the fibrous web,said flock fibres having an uncrimped length no greater than inch andbeing substantially shorter than the web fibrescomposingsaid Web, saidflock fibres being entangled with the web fibres by virtue of the crimpin said flock fibres, said crimped flock fibres extending generally atright angles to the plane of said web and being substantially completelyembedded in said Web, thereby bonding the web fibres in place andimparting strength to said fabric.

2. A nonwoven fabric as in claim 1 wherein the web fibres areheterofilaments having at least one potentially adhesive componentbonded to the flock fibres at the cross-over points between fibres.

3. A process for enhancing the strength of nonwoven fabrics comprising:substantially completelyembedding potentially crirnpable fiock fibresinto a preformed, nonwoven web by projecting the flock-fibres into saidweb by the action of electrostatic forces and subsequently entanglingthe flock fibres with the web fibres by developing crimp in the flockfibres, thereby bonding the Web fibres in the nonwoven fabric andenhancing the strength of the nonwoven fabric.

4. A process as in claim 3 wherein the flock fibres are projected intothe web in a direction generally perpendicular to the plane of the web.

5. A process as in claim 3 wherein the web, with the flock fibresembedded therein, is mechanically compacted prior to developing thecrimp in said flock fibres.

References Cited UNITED STATES PATENTS 6/1962 Breen l6ll77 4/1967 Perril56279

